1. Field of the Invention
The invention relates to a transfer foil, transfer method, and transfer apparatus used in manufacturing of a fluorescent screen of a flat cathode-ray tube.
The present invention also relates to a flat cathode-ray tube for reproducing video information by illuminating a fluorescent layer by an electron beam, and a method of manufacturing the same.
2. Description of the Related Art
A reflection type or transmission type flat cathode-ray tube is known. For example, the reflection type flat cathode-ray tube is noted for its low manufacturing cost and high image quality. In this kind of flat cathode-ray tube, a fluorescent screen is formed on the screen panel inner side disposed at a position confronting a front panel. The fluorescent screen is prepared by forming a fluorescent screen on a reflective layer. In other known example of fluorescent screen, a transparent grid (ITO film), a reflective layer (TiO2 film) and a fluorescent layer are formed in this sequence.
In a known example of a method for manufacturing a fluorescent screen of such flat cathode-ray tube, when composing the fluorescent screen by forming a transparent grid (ITO film), a reflective layer (TiO2 film) and a fluorescent layer sequentially on the inner side of a screen panel, the reflective layer (TiO2 film) and fluorescent layer are formed by a transfer method, and the transparent grid (ITO film) is formed by an application method (see Japanese Laid-open Patent No. 11-96948).
In other example of a method for manufacturing a fluorescent screen of a flat cathode-ray tube, an aluminum film composed of fluorescent layer and reflective layer is formed on a PET (polyethylene terephthalate) film, and the fluorescent screen composed of the fluorescent layer and reflective layer is transferred on the inner side of a screen panel after peeling process. Herein, the fluorescent layer is formed by screen printing, and the aluminum film is formed by screen printing of aluminum paste or vapor deposition. By making use of such transfer process, the fluorescent screen can be manufactured in a small facility, and the manufacturing process can be simplified.
In a conventional transfer method, a transfer foil is prepared by laminating a peeling layer, a fluorescent layer, a reflective layer, and an adhesive layer on a transfer film of PET or the like. This transfer film is adhered to a specified position at the inner side of the screen panel by the adhesive layer. Later, the transfer film is peeled off, and the peeling layer is vaporized at high temperature and removed. Through such transfer process, the fluorescent screen is formed at the inner side of the screen panel.
However, the former manufacturing method of fluorescent screen involved the following problems. First, a large manufacturing equipment is needed because the transfer and application are carried out in different processes. Second, the resistance value of the transparent grid layer (ITO film) may vary due to uneven application, and if attempted to apply uniformly to avoid such possibility, when applied thickly, the film may be turbid and not transparent due to effect of humidity, or when applied thinly, the resistance may be high and conduction may not be sufficient. Therefore, for example, when applied thickly, it is necessary to dry immediately after application, and there are various problem in management.
In the latter manufacturing method of fluorescent screen, the transfer foil used in forming the fluorescent screen is usually manufactured so as to form its reflective layer and fluorescent layer sequentially in a same pattern. However, for example, when each layer is formed by screen printing, the reflective layer on the fluorescent layer may sag in the peripheral area to spread wider than the fluorescent layer. By using such transfer foil, when the fluorescent screen is formed at the inner side of the panel of the cathode-ray tube, since the reflective layer spreads wider than the fluorescent layer, when the image is displayed, the periphery of the reflective layer may reflect significantly, or the color of the reflective layer may appear like a frame, and the display quality of the cathode-ray tube may be extremely lowered. Still more, it is necessary to manage the manufacturing process of the transfer foil, and the working efficiency is lowered.
To manufacture the reflective layer, by using a transfer foil formed by screen printing of aluminum paste composed of aluminum particles and binder, when the fluorescent screen is formed by transfer method, only a reflective layer poor in reflection efficiency is obtained. When using transfer foil forming the reflective layer by an aluminum vapor deposition film, although it is excellent in reflection efficiency, when the adhesive layer is vaporized in the heat treatment process after transfer, the gas is shielded by the aluminum vapor deposition film and cannot escape, and hence the aluminum vapor deposition film may be swollen and ruptured.
Although various improvements have given to the conventional transfer method, the transfer apparatus is unchanged, and only the white stamp is used. That is, the conventional transfer apparatus comprises a table on which a screen panel is mounted as the work, means for supplying a roll of transfer foil, and an elastic rubber for applying heat and pressure to press the transfer foil onto the screen panel. The transfer foil is supplied to the screen panel placed on the table, and is pressed by the elastic rubber, and thereby the transfer foil is transferred.
However, since the screen panel is made of glass, the pressure may be applied unevenly when transferring, the screen panel may be broken, or the transfer foil may be creased, and it has been difficult to transform uniformly.